1. Field of the Invention
The present invention pertains to pressure fluid actuable clutches. More particularly, the present invention relates to clutches wherein the fluid pressure acts upon a piston within the pressure plate assembly. One embodiment of the invention pertains to an application of the fluid-operated clutch in a drag-racing automotive environment wherein the desired controlled slippage of the clutch is achieved by a pneumatic circuit including pneumatic timers.
2. Discussion of the Prior Art
Clutches are employed in a variety of machinery and motorized vehicles to selectively engage and disengage a driving member such as a flywheel of an engine with a driven member such as an output shaft connected to the transmission of an automobile. The rate at which the clutch converts or transfers from a fully disengaged position to a fully engaged position is one of the important specifications in clutch design.
Clutches, such as are used in automotive applications, typically have a flywheel mounted directly to an engine crankshaft and a pressure plate bolted to the flywheel, at a spaced distance. Coaxially located between the pressure plate and the flywheel are one or more clutch plates which are mounted on an output shaft. To engage the clutch, a component of the pressure plate is moved toward the flywheel causing frictional engagement with the clutch plates. As the pressure plate component is moved with progressive force toward the flywheel, the degree of frictional engagement increases. To disengage the clutch, the pressure plate component is moved away from the clutch plates and the frictional engagement decreases. The pressure plate movement is controlled by a spring-biased clutch pedal and associated linkage including a throw-out bearing. The throw-out bearing bears against a dish-shaped spring on the pressure plate. As the throw-out bearing is brought toward the pressure plate, it engages with the center portion of the dish-shaped spring and causes the outer portion of the spring to pivot away from and disengage from the clutch plate. Similarly, as the throw-out bearing is brought away from the dish-shaped spring of the pressure plate, the spring can return to its relaxed state wherein the outer portion of the spring engages with the clutch plate.
As can be appreciated, with mechanical components which repeatedly frictionally engage and disengage with one another, the components wear and decrease in size over time. However, the amount of travel of the dish-shaped spring is fixed; so the degree of engagement of the clutch will change over time due to the wear of the components unless an adjustment is made or the wear is compensated for. In addition, the position of the throw-out bearing must be accurately adjusted for proper clutch operation. Further, the manufacture and assembly of the linkage, throw-out bearing and pressure plate are time consuming.
In the specific application of top classes (top fuel) of modern drag-racing of automobiles, the requirements for a clutch are different than for a passenger automobile. For example, there is no transmission containing different sized gears in a drag-racing vehicle. Instead, the clutch is designed to engage gradually to prevent a loss of traction of the tires against the racetrack due to the application of a 4000 to 5000 horsepower engine to the drive train. In addition, the operation of the clutch is automatic in response to the throttle pedal. Thus, the clutch employed in drag-racing is a variation of the above-described clutch. The dish-shaped washer of the pressure plate is replaced with a plurality of fingers pivotally mounted on a pressure plate assembly. As the engine and pressure plate rotate at progressively greater speeds, centrifugal force acts upon the pivotally mounted fingers and serves to pivot them until a first end of the fingers contacts the clutch plate. A throw-out bearing is selectively engageable with a second end of the fingers to resist the above-described pivoting and prevent engagement with the clutch plate. As the throw-out bearing moves away from the pressure plate, the degree of engagement can increase. The movement of the throw-out bearing away from the pressure plate is controlled by an air-timer circuit.
Each of the pivotally mounted fingers may be of a different size and weight so that the effect of the centrifugal force upon each finger is different. Accordingly, the degree of engagement of the clutch varies with the rotational speed of the engine. Thus, prior to each race an assortment of differently sized and weighted fingers may be installed on the pressure plate to give a desired configuration or to "program" the clutch engagement. As can be appreciated, this controlled-slippage clutch retains many of the inherent drawbacks of the basic automotive clutch. Namely, the throw-out bearing is a key component requiring precise adjustment and positioning and causing problems due to wear. In addition, as the clutch components wear, adjustment or compensation is necessary.
This modified clutch used in drag-racing has some additional limitations. The degree of engagement is necessarily a function of the engine speed, which may not be desirable. For example, if the engine speed accelerates at a less than optimal fashion tending to reduce performance, the degree of clutch engagement will be reduced as well further exacerbating the performance problem. In a contrary fashion if, due to a tune-up for example, the engine accelerates at a greater than expected rate, the degree of engagement of the clutch may progress at a greater rate than desired possibly resulting in the spinning of tires which is extremely undesirable in drag racing. Furthermore, the centrifugal fingers are susceptible to mechanical failure and require time between races for adjustment in order to provide a given racing configuration. Also, the pressure plate assembly with the centrifugal fingers is relatively heavy. Lastly, and perhaps most importantly, the clutch reaction time utilizing centrifugal fingers is greater than desired.
It is against this background and with a desire to provide a clutch without the limitations of the prior art that the apparatus embodying the present invention has been created.